I do a lot of sustained climbing and long rides. I try to sit a lot but then make a point of standing periodically, even if I don't have to to take a butt break and to change my posture. But if I'm struggling up a climb I will often count pedal strokes and I'll stand as much as 1 third of the time. Often I'll go up 2 or even 3 gears, stand for 50 pedal strokes then sit down again. It breaks up the climb in my head and allows me to change tempo and deal with fatigue.
Living life like there's no tomorrow.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS